This invention relates to welding electrodes and particularly relates to an elongated welding electrode suitable for plasma arc welding with a relatively simple welding gun.
In a welding operation, a plasma phenomenon occurs at the welding point in which a portion of the front end of a consumable welding electrode and the immediate area of of the material being welded are transformed into a fluid state. The molten metal in this fluid state subsequently solidified to form the weld metal. In order to achieve a high degree of plasma phenomenon, a welding energy density of 10.sup.5 to 10.sup.6 watts per square centimeter (w/cm.sup.2) must be provided whereas only an energy density of 10.sup.3 to 10.sup.4 w/cm.sup.2 can only be provided in the common welding operation. Theoretically energy density can be increased by reducing the cross sectional size of the welding electrode to a small size such that the welding energy is concentrated within a small surface area. However, due to the high temperature which is normally over 4000.degree. C. generated in the welding operation, a small size electrode and flux coating material thereon would become molten instantly without the formation of a plasma arc required to produce a high quality weld. Accordingly, such method is not feasible.
Heretofore, the most successful method of producing a large plasma arc is by injecting a shielding gas at the welding area through a nozzle provided at the front end of the welding apparatus. The gas, supplied from a compressed gas tank, forms a shield around the front end of the welding apparatus to assure the formation of the plasma arc and it also provides the cooling function of the molten portion of the welding electrode and the immediate area of the welding object to form the solidified weld metal. The main drawback of such method is that the nozzle of the welding apparatus often quickly breaks down due to the exposure to the extremely high welding temperature. Moreover, the construction of the nozzle is complex and since it is critical to assure a precise amount of gas is provided to without causing an incompatible amount of the compressed gas to mix with the plasma arc so as to result in the formation of irregular welds. Furthermore, since the melting of the weld metal and the production of the plasma arc cannot be produced with a single current simultaneously, it is necessary to supply separate currents for providing these functions. Still furthermore, in order to assure the production of a large plasma arc, a large amount of compressed gas must be provided at the welding area. This requires the introduction of separate feeding channels in the welding apparatus wherein one channel is for delivering the electrode to the welding area, and the other channel is for delivering the compressed gas thereto. The use of such compressed gas in the high temperature welding environment presents potential safety and fire hazards. For the above reasons, the construction of the welding apparatus becomes very complex and it is extremely costly to fabricate in order that it can provide the numerous functions demanded by the operation.